The invention relates to an acceleration and deceleration sensor which can be used, in particular, for safety devices in motor vehicles. Such safety devices are comprised, for example, of a bag which can be inflated with compressed air and is disposed in the region of the steering wheel. In the case of a collision, this bag is inflated suddenly and prevents the driver from being thrown onto the steering wheel. The compressed air required to inflate the bag is carried in a compressed air tank which is normally sealed by means of a magnetic valve. In the case of a collision, the magnetic valve is opened, thus providing a path for the compressed air so that the air can flow from the reservoir tank into the above-mentioned bag. The magnetic valve may here be actuated, i.e. opened, by means of the sensor of the present invention. The sensor itself is comprised of an electrical switch as well as an inertial mass which actuates the switch and is displaceable in the direction of the acceleration and deceleration, respectively.
Acceleration and deceleration sensors of the above-mentioned type are described, for example, in German Laid-Open Patent Application No. 2,644,606 or in German Pat. No. 3,216,321. These prior art sensors include an electrical switch in the form of a reed switch which is disposed in the effective range of a permanent magnet system, with the permanent magnet system being an inertial mass which is displaceable in the direction of the acceleration or deceleration.
In the device of Laid-Open Patent Application No. 2,644,606, the permanent magnet system is an individual annular magnet which has a central opening that is placed onto a supporting pipe. The magnet is displaceable on the supporting pipe in the direction of the pipe, which direction coincides with the longitudinal axis of the ring magnet. In the interior of the supporting pipe, there is provided a reed switch which is arranged in such a manner that it is normally disposed outside the effective range of the permanent magnet and whose contact tongues are therefore normally open. If an acceleration or deceleration acts on this arrangement, the permanent magnet is displaced against the force of a spring so that it moves into the range of the reed switch. The field of the permanent magnet then magnetizes the contact tongues of the reed switch and closes them. When the acceleration or deceleration is terminated, the spring moves the permanent magnet back into its original position, thus opening the reed switch again.
In the arrangement disclosed in German Pat. No. 3,216,321, the permanent magnet system is a rod magnet which is mounted, due to its different spatial configuration, in a tubular housing. A reed switch is arranged in the wall of the tubular housing in such a manner that the reed switch is normally disposed outside the circle of action of the permanent magnet. If an acceleration or deceleration acts on the arrangement the rod-shaped permanent magnet is displaced, causing its field to move into the vicinity of the reed switch. The switching tongues of the reed switch are thus magnetized and closed. If the acceleration or deceleration is high enough, the permanent magnet will finally abut against a spring which is compressed by the force exerted on it in this way. After the acceleration or deceleration is terminated, the spring is relaxed again and pushes the rod magnet back until the rod magnet finally again takes up its original position if the recoil force of the spring was large enough.
It has been found that acceleration and deceleration sensors, in which the magnet system is comprised of an individual permanent magnet in combination with a mechanical spring, exhibit drawbacks. The springs require a certain minimum force for compression, thus limiting the effective range of the sensors. Additionally they considerably impede the switching or pulse times and they have the additional drawback that the particularly soft and easily compressible springs have a tendency to be damaged during the compression and, under certain circumstances, are deformed permanently.